The improved apparatus and process of the present invention is broadly applicable to the processing of organic carbonaceous materials under controlled pressure and elevated temperatures to effect a desired physical and/or chemical modification thereof to produce the desired product. More particularly, the present invention is directed to the processing of such carbonaceous materials containing appreciable quantities of moisture whereby a substantial reduction in the residual moisture content of the product is effected in addition to a desired thermal chemical restructuring of the organic material to impart improved properties thereto including increased heating values on a dry moisture-free basis.
The shortages and rising prices of conventional energy sources such as petroleum and natural gas have occasioned investigation of alternative energy sources in plentiful supply such as lignitic-type coals, cellulosic materials such as peat, waste cellulosic materials, such as sawdust, bark, wood scrap, branches and chips derived from lumbering and sawmill operations, various agricultural waste materials, such as cotton plant stalks, nutshells, corn husks and the like. Unfortunately, such alternative materials in their naturally occurring state are deficient for one or a variety of reasons for use directly as high energy fuels. For this reason, a variety of processes have been proposed for converting such materials into a form in which their heating value on a moisture-free basis is substantially enhanced, in which they are stable and resistant to weathering during shipment and storage and in which the upgraded fuel product can more readily be adapted for use in conventional furnace equipment.
Typical of such prior processes are those described in U.S. Pat. No. 4,052,168 by which lignitic-type coals are chemically restructured through a controlled thermal treatment providing an upgraded carbonaceous product which is stable and resistant to weathering as well as being of increased heating value approaching that of bituminous coal; U.S. Pat. No. 4,127,391 in which waste bituminous fines derived from conventional coal washing and cleaning operations is treated to provide solid agglomerated coke-like products suitable for direct use as a solid fuel; and U.S. Pat. No. 4,129,420 in which naturally occurring cellulosic materials such as peat as well as waste cellulosic materials are upgraded by a controlled thermal restructuring process to produce solid carbonaceous or coke-like products suitable for use as a solid fuel either by itself or in admixture with other conventional fuels. An apparatus and process for achieving an upgrading of such carbonaceous materials of the types set forth in the aforementioned U.S. patents is disclosed in U.S. Pat. No. 4,126,519 which is assigned to the assignee of the present invention.
In accordance with the teachings of U.S. Pat. No. 4,126,519, the substance of which is incorporated herein by reference, an organic carbonaceous material is introduced in the form of an aqueous slurry which is pressurized and conveyed in a continuous manner from a conveying chamber to a reaction chamber while in countercurrent heat transfer relationship with a gaseous phase generated in the reaction stage to effect a preheating of the feed material. The pressure and temperature in the reaction chamber is controlled in further consideration of the residence time to effect a desired thermal treatment of the feed material which may include the vaporization of substantially all of the moisture therefrom as well as at least a portion of the volatile organic constituents therein while simultaneously undergoing a controlled partial chemical restructuring thereof. The hot reaction mass is retained in a nonoxidizing environment whereafter it is cooled to a temperature at which it can be discharged from the apparatus in contact with the atmosphere.
While the apparatus and method as disclosed in U.S. Pat. No. 4,126,519 has been found eminently suitable for treating organic carbonaceous materials to effect a conversion thereof into improved carbonaceous products, it has been observed that the efficiency and capacity of the system is somewhat limited by the moisture content present in the carbonaceous feed material and that the waste water extracted from the equipment contains dissolved organic constituents some of which are environmentally unfavorable necessitating waste water treatment before they can harmlessly be discharged to waste. While the process produces by-product gases in quantities sufficient to meet the thermal requirements of the process providing a self-sustaining operation, it has further been found that feed materials containing excessive moisture contents detract from the thermal efficiency of processing such materials. The foregoing problems are particularly pronounced in connection with organic carbonaceous materials having inherently high moisture contents, such as for example, peat which in an as-mined or as-dredged condition may contain up to as high as 92 percent by weight moisture. Even when such peat is preliminarily air dried to reduce its moisture content to about 50 percent by weight, the thermal efficiency and output capacity of the processing apparatus are less than optimum from an economical standpoint and have somewhat detracted from a more widespread commercial adaptation of the system.
It is, accordingly, an object of the present invention to provide an improved apparatus and process which is capable of processing carbonaceous feed materials of inherently high moisture content by effecting an efficient in situ reduction in the water content of the input feed stock during processing whereby substantial increases in the thermal efficiency and output capacity of the process are attained with corresponding improvements both in the economical operation of the process itself as well as in any required waste water treatment resulting from the process, thereby further enhancing the commercial adaptation of such equipment and processing techniques as a viable alternative source of energy.